Explosive of reduced capacity containing siliceous foam particles

ABSTRACT

Explosives of reduced capacity in the form of powders, semiplastic, plastic or slurries having a content of a filler which does not take part in the explosive reaction during detonation and will not, therefore, affect the smoke composition.

United States Patent [1 1 Kraemer et a1.

[ July 22,1975

1 1 EXPLOSIVE OF REDUCED CAPACITY CONTAINING SILICEOUS FOAM PARTICLES [75] inventors: Stefan Kraemer, Essen; Alois Seidl,

Thurnstern, both of Germany; Hans-Joachim Riedl, deceased, late of Recklinghausen, Germany, by Herta Emilie Riedl, legal representative [73] Assignee: Wasag Chemie, Munich, Germany [22] Filed: Dec. 19, 1973 [21] Appl. No.: 426,306

Related U.S. Application Data [63] Continuation of Ser. No. 73,625, Sept. 18, 1970,

abandoned.

[52] U.S. Cl. 149/2; 149/21; 149/41; 149/53; 149/110 [51] Int. Cl C06b 19/00 [58] Field of Search 149/2, 21, 53, 41,110

[56] References Cited UNITED STATES PATENTS 7/1972 Cattermole et al 149/2 10/1972 Edwards 149/2 Primary ExaminerStephen .l. Lechert, Jr. Attorney, Agent, or Firm-Hammond & Littell [57] ABSTRACT 5 Claims, No Drawings EXPLOSIVE OF REDUCED CAPACITY CONTAINING SILICEOUS FOAM PARTICLES This is a continuation of Ser. No. 73,625, filed Sept.

18. 1970, now abandoned.

STATE OF THE ART In the normal use of explosives, it is often necessary to use explosives with a reduced capacity or to effect a smaller amount of energy at a given drill hole diameter than is possible with the usual blasting cartridges having a diameter of 25 to 30 mm. When driving tunnels or galleries, the profile thereof can be formed much more true to size if the blasting of the side walls and particularly of the roof is done as carefully as possible, which also reduces the debris accumulated. When the profile is shored up with bricks or by concrete reinforcement, less building materials are required if a neat profile results from the blasting which means reduced construction costs. Similar conditions exist in salt mines where particularly more careful blasting results in more stable roofs.

Various methods have been used to achieve this goal of more careful blasting. One means of reducing the explosive capacity is to reduce the normal cartridge diameter to mm or less. This results in difficulties in packing the much smaller diameter cartridges which is disproportionately expensive and the strength of the thin cartridges declines so much even at medium lengths that an orderly charging of the drill holes cannot be guaranteed. This latter disadvantage is overcome by using plastic or cardboard pipes as the outer shell, but the packing thereof takes ever longer and is more expensive. Moreover, the reduction in the cartridge diameter is limited by the fact that the limiting diameter for thorough detonation of most commercial explosives is relatively high.

Another attempt to reduce the charge density of explosives inserted empty spaces between each two blast cartridges but this so-called cushioned blasting is restricted to use with explosives having a high propagation capacity. Another means of reducing the energy capacity of explosives of a given diameter is admixture of the explosive with an inert substance such as sodium chloride but the resulting blast fumes have a disturbingly high content of hydrogen chloride which is proportional to the amount of sodium chloride used.

Another proposal for reducing the explosive capacity is to dilute the explosive with air or gases by such means as foaming of pasty or slurried explosives. This has been effected by the dispersion of air or gases as in U.S. Pat. No. 3,288,661 or by producing gas or air in the explosive charge as in U.S. Pat. Nos. 3,390,028 and 3.390.030. The big disadvantage of these diluted explosives is that they are not storable and therefore are not usable in the form of a cartridge.

Swiss Pat. No. 446.156 proposes adding particles of organic plastic foam such as Styropor, etc., to explosive charges which produces a fairly satisfactory result. However, the organic particles take part in the detonation reaction and impair the oxygen balance whereby the carbon monoxide content of the detonation fumes are greatly increased. This increase prevents extensive blasting underground or in difficult to ventilate galleries with these explosives. Attempts to use inorganic foam fillers have not been successful as foams such as Perlites, Vermiculites, etc., posses too great an absorptive capacity for liquid explosive components or foams such as foamed water glass have a too high alkalinity which changes the explosive.

OBJECTS OF THE INVENTION It is an object of the invention to provide a novel explosive charge having a reduced capacity.

It is a further object of the invention to provide novel explosive charges containing a filler which does not take part in the detonation reaction and will not change the composition of the detonation fumes.

These and other objects and advantages of the invention will become obvious from the following detailed description.

THE INVENTION The novel explosive charges of the invention having a reduced explosive capacity are comprised of an explosive in the form of a powder, a slurry or a semiplastic or plastic mass and a content of filler particles which do not take part in the detonation reaction and will therefore not influence the fume composition, particularly the carbon monoxide content.

Examples of suitable filler particles for the compositions of the invention are foamed glass or other foamed siliceous products of natural or synthetic origin having a bulk density of 0.03 to 0.25, preferably less than 0.1.

Among the preferred particles are those prepared by the process of copending commonly assigned U.S. Patent application Ser. No. 788,800 filed which comprises dissolving approximately 0.02 to 0.7 parts by weight of fibrous inorganic silicate in one part by weight of an aqueous alkalimetal silicate solution, evaporating the resulting mixture to a water content of 5 to 20 percent by weight by heating, granulating the dried material to a particle size of about 0.5 to 20 mm, coating the granulated material with a dispersion of a high melting inorganic compound having a melting point between about l,200 to 2,500C and heating the coated granulate to about 600 to 1,000C to produce foamed glass particles melting between about 500 to 900C.

Another preferred method of producing the foam glass like bodies is described in copending, commonly assigned U.S. Patent application Ser. No. 724,634 filed Apr. 26, 1968 which comprises dissolving powdered silicatic containing material which may also contain a blowing agent and at least one member selected from the group consisting of boron compounds and metal oxides in an aqueous alkali metal silicate solution in a ratio of 0.02 to 0.8 to 1.0 based on the said alkali metal silicate, evaporating the solution to dryness, comminuting the residue to a particle size of not more than 2 mm and heating the resulting powder to 650 to l,000C to form glass-like porous molded bodies, the dissolution of the silicatic containing material being effected by a method selected from the group consisting of wet milling and agitation at a rate which prevents deposition of the said material. The particles produced by the said two processes are spherical in shape with a diameter of 0.1 to 10 mm.

The said fillers can be added to all conventional powdery, semi-plastic, plastic or slurried explosives and are usually added in an amount of 10 to percent by weight of the final composition. In a modification of the invention, the said fillers can be made hydrophobic or hydrophilic by conventional means, depending upon the type of explosive. For example, foam granules which are to be used in an aqueous explosive slurry can be made hydrophobic by impregnation with an acetone solution of a silicone oil to prevent water from impregnating the foam granules.

In the following examples there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

EXAMPLE I A plastic explosive of the type Amongelit having the composition of 29 percent by weight of nitroglycerin, 8 percent by weight of di-trinitriotoluol. 1 percent by weight of soluble gun cotton. 2 percent by weight of wood powder and 60 percent by weight of ammonium nitrate had an explosive density of l.5 to 1.6 gm/cc. The addition of 500 cc of a spherical foam granulate having a bulk density of 0.8 and a charge volume of about 55 percent to l kilogram of the said explosive reduced the explosive density from about 1.55 to about 1.15 gm/cc. The addition of 750 cc of the said foam granulate to each kilogram of said explosive decreased the explosive density to 0.96 gm/cc.

The explosive efficiency based on weight remains constant as seen from the Trauzl block expansion of 400 cc. However, the explosive efficiency based on the volume decreased in the ratio of about 100 (no addition); 75 (addition of 500 cc); 60 (addition of 750 cc). The blast fumes under equal confinement and equal advance explosion conditions remain unchanged.

EXAMPLE ll A slurry explosive in the form of a watery mud had the composition of 55 percent by weight of ammonium nitrate. 9 percent by weight of sodium nitrate. 25 percent by weight of aluminum, 1 percent by weight of guar flour and 10 percent by weight of water and had an explosive density of about 1.35 gm/cc. The addition of 500 cc of the foam granulate of Example I to one kilogram of the said explosive reduced the explosive density to about 1.0 gm/cc and the addition of 750 cc of granulate reduced the explosive capacity to about 0.9 gm/cc.

The impregnation of the foam granulate with an acetone solution of silicone oil before adding it to the slurry makes the foam granules hydrophobic whereby a minimum of the water in the saturated salt solution or explosive slurry penetrates the granules. Slurries containing TNT or other explosives can be made porous in the same way with the said foam granules.

It is surprising that the critical cartridge diameter or charge diameter (the smallest diameter at which complete detonation still occurs) is not increased but is often decreased under comparable confinement and advance explosion conditions.

Various modifications of the compositions of the invention may be made without departing from the spirit or scope thereof and it is to be understood that the invention is to be limited only as defined in the appended claims.

We claim:

1. A novel explosive charge having a reduced explosive capacity comprising an explosive in the form of a powder, a slurry or a semi-plastic or plastic mass and a content of porous filler particles which do not take part in the detonation reaction and will, therefore, not influence the fume composition, particularly the carbon monoxide content, said filler particles being selected from the group consisting of foam glass particles melting between 500 and 900C and other foamed silicate containing products of synthetic origin, said particles being spherically shaped with a diameter of 0.1 to 10 mm and having a bulk density of 0.3 to 0.25.

2. The explosive charge of claim 1 wherein the bulk density of the particles is less than 0.1 g/cc.

3. The explosive charge of claim 1 wherein the particles are 10 to percent by weight of the explosive charge.

4. The explosive charge of claim 1 wherein the particles are made hydrophobic.

5. The explosive charge of claim 1 wherein the particles are made hydrophilic. 

1. A NOVEL EXPLOSIVE CHARGE HAVING A REDUCED EXPLOSIVE CAPACITY COMPRISING AN EXPLOSIVE IN THE FORM OF A POWDER, A SLURRY OR A SEMI-PLASTIC OR PLASTIC MASS AND A CONTENT OF POROUS FILLER PARTICLES WHICH DO NOT TAKE PART IN THE DETONATION REACTION AND WILL, THEREFORE, NOT INFLUENCE THE FUME COMPOSITION, PARTICULARLY THE CARBON MONOXIDE CONTENT, SAID FILLER PARTICLES BEING SELECTED FROM THE GROUP CONSISTING OF FOAM GLASS PARTICLES MELTING BETWEEN 500* AND 900*C AND OTHER FOAMED SILICATE CONTAINING PRODUCTS OF SYNTHETIC ORIGIN, SAID PARTICLES BEING SPHERICALLY SHAPED WITH A DIAMETER OF 0.1 TO 10 MM AND HAVING A BULK DENSITY OF 0.3 TO 0.25.
 2. The explosive charge of claim 1 wherein the bulk density of the particles is less than 0.1 g/cc.
 3. The explosive charge of claim 1 wherein the particles are 10 to 90 percent by weight of the explosive charge.
 4. The explosive charge of claim 1 wherein the particles are made hydrophobic.
 5. The explosive charge of claim 1 wherein the particles are made hydrophilic. 